Design and Construction of Solar Dryer for Drying Agricultural Products

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1946
Design and Construction of Solar Dryer for Drying Agricultural
Products.
Prof. Pravin M. Gupta1, Amit S. Das2, Ranjit C. Barai3, Sagar C. Pusadkar4, Vishal G. Pawar5.
1Assistant Professor,Dept. of Mechanical Engineering, J.D.C.O.E.M, Nagpur.
2345Students, Dept. of Mechanical Engineering, J.D.C.O.E.M, Nagpur.
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Abstract-The solar drying system utilizes the solar energy
to heat up a air and to dry any food substance which is loaded,
which is not only beneficial but also it reduces wastage of
agricultural products and helpsinpreservationofagricultural
products, but it also makes transportation of such dried
product easily and promotes the health and welfare of the
people. This paper presents the design and construction of a
solar dryer for drying a agriculture product. The dryer is
composed of solar collector (air heater) with the baffles and a
solar drying chamber containing rack of four net trays both
being assimilated together. The air allowed in through air
inlet is heated up in the solar collectorchamberandchanneled
through the drying chamber where it is utilized in drying
(removing of the moisture content from thefoodsubstancesor
agricultural product which is loaded in it). The design was
based on the geographical location which is Nagpur and
meteorological data were obtained for proper design
specification. Locally materials were used for theconstruction
are wood, glass, aluminium metal sheet and net for the trays.
Introduction
Drying is an excellent way to preserve foods. Drying was
probably the first ever food preserving method used by
mans. It involves the removal of moisture from agricultural
product so as to provide a product that can be safely stored
for longer period of time.
“Sun drying” is the earliest method of drying farm
produce ever known to man and it involvessimplylayingthe
agricultural products in the sun on mats, roofs or drying
floors. This has several disadvantage since the farmproduce
are laid in the open sky and there is greater risk of spoilage
due to adverse climatic situation like wind, rain, moist and
dust, loss of product to insects, birds and rodents; totally
dependent on good weather and very slow drying rate with
danger of mould growth thereby causing deterioration and
decomposition of the product. The process also requires
large area of land, takes time and highly labour intensive.
In solar drying, solar dryers are specialized devices that
control the drying process and protect agricultural product
from damage by insect, dust and rain. In addition, it takes up
less space, takes less time and relatively inexpensive
compared to artificial mechanical drying.Thesolardryer can
be seen as one of the solutions to the world’s food and
energy crises. With drying, most agricultural product can be
preserved and this can be achieved more efficiently through
the use of solar dryer.
Some Background to the Concept
Attempts to Harness Solar Energy
The idea of using solar energy to produce high
temperature dates back to classical times. The solar
radiation has been used by man since the starting of timefor
heating his domicile, for agricultural purposes and for
personal uses. Reports abound in literature on the 18th
century works of Archimedesonapplyingthesun’srayswith
flat mirrors; Antoine Lavoisier on solar furnace; Joseph
Priestly on applying rays using lens. In the 19th century,
improvement of solar distillation unit covering 4750sq
meters of land, operated for 40 years and, generating
22712.47 liters of water from salt water per day has been
reported. Also, John Ericson’s work on conversion of solar
energy into mechanical energy through a device, which
produced 1hp (746 W) for each 9.3m2 of collecting surface
has also been reported.
Modern research on the use of solarenergystartedduring
the 20th century. Improveent includetheinventionofa solar
boiler, small powered steam engines and solarbattery,butit
is hard to market them in competition with engines running
on inexpensive gasoline. During the mid 1970’s shortages of
oil and natural gas, increase in the cost of fossil fuels and the
reduction of other resources energize efforts in the United
States to develop solar energy into a practical power source.
Thus, interest was rekindled in the comparison to natural
“sun drying”, solar dryers generate higher temperatures,
lower relative humidity,lowerproductmoisturecontentand
reduced spoilage during the drying process. Thus, solar
drying is a better alternative solution to trapping of solar
energy for heating and cooling, the generation of electricity
and other purposes.
Capturing Solar Energy
Solar radiation can be transfer either into thermal energy or
into electrical energy. This can be done by useing of thermal
collectors for conversion into heat energy or photovoltaic
collectors for conversion into electrical energy. Two main
collectors are used to save solar energy and convert it to

thermal energy, these are flat plate collectors and
concentrating collectors. In this paper, significance is laid
much on the flat plate collectors which are also known as
non-focusing collectors.
Importance of Solar Dried Food
For centuries, people of different nations havebeen
preserving fruits, other crops, meat and fishes by drying.
Drying is also useful for hay, copra, tea and other income
producing non-food crops. With solar drying beingavailable
everywhere, the presentability of all these farm producecan
be greatly rising. It is worth noting that until around the end
of the 18th centurywhencanning wasdeveloped,drying was
essentially the only method of food preservation.
The energy input for drying is less than what is
required to freeze or can, and the storage space is minimal
compared with that required for canning jars and freezer
containers. It was further stated that the nutritional value of
food is only nominal affected by drying. Also, food scientists
have found that by decreasing the moisture content of food
to 10 to 20%, bacteria, yeast, mold and enzymes are all
protected from spoiling it. Microorganisms are effectively
killed when the internal temperature of food reaches 150°F.
The flavour and most of the nutritional value of dried food is
protected and concentrated. Dried foods do not require any
special storage equipment and are easy to transporting.
Dehydration of vegetables and other food crop by general
methods of open-air sun drying is not satisfactory, because
the products deteriorate fastly.
Studies showed that food items dried in a solar dryer were
exclusive to those which are sun dried when evaluated in
terms of taste, colour and mould counts. Solar driedfoodare
quality products that can be stored for extended periods,
easily transported at minimum cost while still providing
excellent nutritive value. This paper therefore presents the
design nd construction of solar food dryer for drying
agricultural product.
Material and Method
General Description of the Solar Dryer
The most commonly seen design types are of
cabinet form (wooden boxes with glass cover), some types
are even modified making use of cardboard boxes and non
reflecting nylon or polythene.
For the design being considered, the greenhouse
effect and thermosiphon principles are the theoretical basis.
There is an air vent (or inlet) to the solar collector where air
goes inside and is heated up by thegreenhouse effect,the hot
air rises through the drying chambergoingthroughthetrays
and around the food, removing all moisture content and
exits through the exhust fan at the top of cabinet.
The solar food dryer consists of two major
compartment or chambers being integrated together:
1. The solar collector compartment, which can also be
referred to as the air heater of system.
2. The drying chamber, designed to accommodate four
layers of drying trays made of net (cheese cloth) on
which the product (or food) are placed for drying.
Materials Used
The following materials were used for the
construction of the domestic solar dryer:
1. Wood – wood was selected for for entire casing, because
it is light in weight, easily available and cheaper in cost
then other material.
2. Glass – we choose the glass for upper covering of the air
heater chamber because it is easily allow the rays togo
inside and heat the sheet and it resist the heat to go out
side.
3. Aluminium sheet of 1mm thickness use to increase the
temperature of air passing through the air chamber
painted black with tar for absorption of solar radiation.
4. Net used for constructing the trays for placingtheproduct
in the drying chamber.
5. Nails,glue and silicon glue as fasteners and adhesives.
6. Insect net at air inlet and outlet to restrict the insect to
enter inside the chamber.
7. Hinges and handle for the dryer’s door and reflector.
8. Paint (black and brown).
9. Plan Reflecting mirrors (two).
Design Consideration
1. Temperature - The minimum temperature for drying
food is 35°C and the maximum temperature is 65°C,
therefore. 50°C and above is considered average and
normal for drying fruits, vegetables, roots and tuber
crop chips, crop seeds,etc.

2. The design was made for the optimum temperature for
the dryer. T0 of 65°C and the air inlet temperatureorthe
ambient temperature of dryer was T1 = 35°C
(approximately outdoor temperature).
3. Efficiency - This is defined as the ratio of the useful
output of a product to the input of the product.
4. Air gap - It is suggested that for hot climate passive
solar dryers, a gap of 10 cm should be createdasairvent
(inlet) and air passage.
5. Glass and flat plate solar collector – It suggested that
the glass covering should be 4-5mm thickness. In this
work, 5mm thick transparent glass was used. It also
suggested that the metal sheetthicknessshouldbeof0.8
– 1.0mm thickness; here a aluminium of 1.0mm
thickness was used.
6. Dimension – It is recommended that a constant
exchange of air and a roomy drying chamber should be
attained in solar food dryer design, thus the design of
the drying chamber was made as spacious as possibleof
average dimension of 50 × 47 × 45cm with air passage
(air vent) out of the cabinet of 50 × 5cm2.
7. Dryer Trays – Net(metal) was selected as the dryer
screen or trays to aid air circulation within the drying
chamber. Three trays were made of metal net. The tray
dimension is 48 × 48cm.
8. Exhust fan of 12v is used to remove the air from the
drying chamber.
The design of the dry chamber making use of
wooden wall sides and a top protects the food to be placed
on the trays from direct sunlight since this is undesirable
and tends to bleach colour, removes flavour and causes the
food to dry unevenly.
Design Calculations[7]
1. Solar Collector/Air Heater Angle of Tilt (β).
It states that the angle of tilt (β) of the air heater should be
β = 100 + lat ф ………………… (1)
were lat ф is the latitude of the collector location, the latitude
of Nagpur where the dryer was designed is latitude 21.150N.
Hence, the suitable value of β use for the collector:
β = 100 + 21.150 = 31.150
2. Insulation on the Collector Surface Area.
A research obtained the value of insolation for Nagpur i.e.
average daily radiation H on horizontal surface as;
H = 657W/m2
and average effective ratio of solar energy on tiltedsurfaceto
that on the horizontal surface R as;
R = 1.017
Thus, insulation on the collector surface was obtained as
Ic= HT = HR =657 × 1.017 = 668.17W/m2 ………. (2)
3. Determination of Collector Area and Dimension.
The mass flow rate of air Ma was determined by taking the
average air speed Va = 0.2m/s.
The air gap height was taken as 5cm = 0.05m and the width
of the collection assumed to be 50cm = 0.5m.
Thus, volumetric flow rate of air
V'a = Va × 0.05 × 0.6
V'a = 0.2 × 0.05 × 0.5 = 5 × 10-3m3/s
Thus mass flow rate of air
Ma =vaρa ………………………. (3)
Density of air ρa is taken as 1.28kg/m3
Ma = 5 × 10-3 × 1.28 = 6.4 × 10-3kg/s
Therefore, area of the collector AC
AC = (6.4 × 10-3 × 1005 × 30)/(0.5 × 668.17) = 0.57m2
The length of the solar collector (L) was taken as;
L = Ac/B = 0.57/0.6 = 0.95m
Thus, the length of the solar collector was taken
approximately as 1m.
Therefore, collector area was taken as (1 × 0.6) = 0.6m2
4. Determination of the Base Insulator Thickness for the
Collector.
The rate of heat loss from air is equal to rate of heat
conduction through the insulation. The following equation
hold for the purpose of the design.
FmaCp (T0 – Ti) = Ka Ac(T0 – Ta )/tb ……… (4)
K = 0.04Wm-1K-1 which is the approximate thermal
conductivity for glass wool insulation.
F = 10% = 0.1
T0 = 65ºC and Ti = Ta = 35ºC approximately
ma = 6.4 × 10-3Kgs-1
Cp = 1005JKg-1K-1
and Ac = 0.57m2
tb =[0.04 ×0.57× (60-30)]/[0.1×6.4×10-3×1005×(60-30)] =
0.0354 = 3.54cm

For the design, the thickness of the insulator was taken as
7cm. The side of the collector was made of wood, the loss
through the side of the collector was considered negligible.
5. Calculation of Heat Losses from the Solar Collector (Air
Heater).
Total energy transmitted and absorbed is given by
IcAcτα = Qu + QL + Qs …………………… (5)
where Qs is the energy stored which is considered negligible
therefore,
IcAcτα = Qu + QL ……………………… (6)
Thus QL the heat energy losses
QL = IcAcτα - Qu …………………………... (7)
Since
Qu = maCp (T0 – Ti) = maCp∆T ……………… (8)
and
QL = ULAc∆T …………………………… (9)
then
ULAc∆T = IcAcτα - maCp∆T ………………. (10)
UL = (IcAcτα - maCp∆T)/(Ac∆T) …………. (11)
α was taken as 0.9 and τ = 0.86
Ta = 0.774
UL = (668.17×0.57×0.774 - 6.4×10-3×1005×30)/(0.57×30) =
(294.78 -192.96)/17.1
UL = 5.9W/m2°C
Therefore,
QL = 5.9 × 0.57 × 30 = 100.8W
This heat loss includes the heat loss through the insulation
from the sides and the cover glass.
Construction
The solar food dryer was generally constructed by wood
because it is easily available and light in weight and cost.
Since the entire casing of wood only the top of air heater
chamber is made of two 5mm glasses, themajorconstruction
works of project is carpentry works.
The following tools were used in measuring and marking out
on the wooden planks:
 Carpenter’s pencil.
 Steel tapes (push-pull rule type).
 Steel meter rule.
 Vernier caliper.
 Steel square.
 Angle plate.
 Scriber.
The following tools were also used during the other
construction;
 Hand saws (crosscut saw and ripsaw).
 Jack plane.
 Wood chisel.
 Hammer.
 Mallet.
 Pinch bar and pincers.
 Electric cutter machine.
The construction was generally made with simple butt joints
using nails as grapnel and glue (adhesive) where necessary.
The construction was sequenced as follows for the wood
work.
 Marking out on the planks to cut into desired shape
size.
 Cutting out the already marked out parts properly.
 Planning of cut out parts to smoothen the surfaces.
Combining and fastening of the cut out parts with nails and
glues.
The metal sheet used was Aluminium of 1mm thickness. It
was cut to the size of 100×50cm to minimize the top heat
loss. It was painted black color for maximum absorption and
radiation of heat energy. The aluminium sheet, together with
the insulator of 5mm thickness, was placed inside the air
heater (solar collector) compartment.
The glass was cut into size of 100 × 50cm size and two of
these were required. One as the solar collector’s cover. The
glass used was clear glass with 5 mm thickness.
The trays were made of steel net and steel net to permit free
flow of air within the drying cabinet chamber and also
geeting heatup. Three trays were used with average of 7cm
spacing arranged vertically one on top of the other, the tray
size was 48 × 48cm.
The interior of the solar food dryer was insulated by heatlon
sheet on this aluminium casing was placed and sheet was
painted black with tar to promote adsorption of heat energy
while the exterior was painted brown to minimize the
adverse effects of weather and insect attack on the woodand
also for aesthetic appeal.
Two reflecting mirrors are used to reflect the sun rays on the
glass properly on 135° and 120° angles for proper reflation,

the thickness of mirrors are 3.5mmtheyarestickedbysilicon
glue. Exhust fan of 6inch diameter and 12v was used to
remove the moist aire from the chamber properly.
IMAGES OF SOLAR DRYER
1.1 Side view of Solar Dryer
1.2 Front view of Solar Dryer
1.3 Back view Of Solar Dryer
1.4 Drying Chamber with Trays
Conclusion
Solar radiation can be highly effectiveandutilizedfordrying
of agricultural product in our environment if proper design
is carried out. This was demonstrated and the solar dryer
designed and constructed expressed sufficient ability to dry
agricultural produce most especially food items to an
appreciably reduced moisture level.
Locally available cheap materials were used in
manufacturing of solar dryer making it available and
affordable to all and specially for farmers. This will go a long
way in reducing food wastage and at the same time food
shortages, since it can be used extensively for majority of the
agricultural food crops. Apart from this, solar energy is

required for its operation which is readily available in the
tropics, and it is also a clean type of energy. It protects the
environment and consume cost and time spent on open sun
drying of agricultural produce since it driesfooditemsfaster.
The food items are also well protected in the solar dryerthan
in the open sun, thus reducing the case of pest and insect
attack and also contamination.
However, the performance of existing solar food
dryers can still be improved upon especially in the aspect of
reducing the drying time and probablystorageofheatenergy
within the system. Also, meteorological data should beeasily
available to users of solar products to ensure maximum
efficiency and effectiveness of the system. Such information
will probably guide a local farmer on when to dry his
agricultural product and when not to dry them.
References
[1]. Scalin D., The Design, Construction and Use of an Indirect,
Through-pass, Solar Food Dryer, Home Power Magazine,
1997, 57, p. 62-72.
[2]. Whitfield D.E., Solar Dryer Systems and the Internet:
Important Resources to Improve Food Preparation, 2000,
Proceedings of International Conference on Solar Cooking,
Kimberly, South Africa.
[3]. Nandi P., Solar Thermal Energy Utilization in Food
Processing Industry in India, Pacific Journal of Science and
Technology, 2009, 10(1), p. 123-131.
[4]. Ayensu A., Dehydration of Food Crops Using Solar Dryer
with Convective Heat Flow, 2000, Research of Department of
Physics, University of Cape Coast, Ghana.
[5]. Sukhatme S.P., Solar-Energy-Principles of Thermal
Collection and Storage, Tata McGraw Hill Publishing
Company Limited, 1996.
[6]. Olaleye D.O., The Design and Construction of a Solar
Incubator, 2008, Project Report, submittedtoDepartmentof
Mechanical Engineering,UniversityofAgriculture,Abeokuta.
[7]. Olayinka ADUNOLA, Design and construction of a
Domestic Passive Solar Food Dryer,2014, department of
mechanical, Nigeria

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